The present invention relates to polarized sunglass lenses with particular vision-enhancing properties.
Recent advances in sunglass lens technology, such as polarized lenses incorporating certain rare-earth compounds, have brought long-desired improvements in perceived color saturation, contrast, and visual acuity. In particular, lenses made in conformance with U.S. Pat. No. 6,145,984 by Farwig demonstrate the advantages of combining light polarization with selective color filtration through the use of a glass composition comprising three particular rare-earth oxides to achieve a remarkable degree of vision enhancement.
Rare-earth oxides are oxides of metals in the lanthanide and actinide series of the periodic table of elements. When incorporated into optical-glass compositions, some of these rare-earth metal oxides impart selective filtering of certain portions of the visible light spectrum.
The Farwig patent discloses points of maximum light transmittance that are located within the blue, green, and red portions of the visible light spectrum (the three additive primary colors upon which human color vision is based) and points of minimum light transmittance located between the points of maximum light transmittance. This type of lens is called “trichroic” because it thus favors the transmittance of the three primary additive colors.
The Farwig patent discloses three examples of trichroic rare-earth glass, each of which could be combined with a polarizer to implement the Farwig lenses. The first of these is Schott S-8807, a neodymium-oxide glass known in the optical industry as Amethyst Contrast Enhancement or “ACE” glass. The second of these is Schott S-8801, which is known as didymium glass. Didymium glass contains oxides of neodymium and praseodymium. The third of these is Schott S-8506, a glass which contains oxides of neodymium, praseodymium, and erbium. None of these glass types effectively block ultraviolet (UV) light at 1 mm thickness and all have very high light transmittance in the near-UV range of 380 nm to 420 nm.
In lenses made according to U.S. Pat. No. 6,604,824 or 6,334,680 by Larson only one rare-earth oxide is employed, namely neodymium oxide. Lenses which use Schott S-8506 glass according to the Farwig patent have a more complex spectral transmittance profile than the Larson lenses due to the two additional rare-earth oxides present in Schott S-8506. The Larson lenses have some similar peak transmittance and absorption bands, but with less pronounced absorption bands. No disclosed formulations of the Larson neodymium glass block UV light to a significant extent. Blocking of UV light in the Larson lenses as disclosed requires the addition of UV-blocking means to at least one layers of the lens structure other than the layer which contains the neodymium oxide.
In polarized lens assemblies of the prior art which incorporate these rare-earth light filters and contrast enhancers as lens elements, dyes or other colorants are typically formulated into the adhesive, polarizer, and/or rear lens element layers to block UV light and near-UV light, to reduce the transmittance of visible light to the desired low levels in the finished laminated lens assemblies, and/or to provide a color tint.
The importance of avoiding excess ocular exposure to UV and near-UV light is well-known in the ophthalmic industry, as these wavelengths have been linked to the development of cataracts and macular degeneration, both of which cause vision loss. It can also be appreciated that the blocking of UV light before it strikes the internal layers of a laminated lens assembly is beneficial in preventing fading and discoloration of UV-sensitive color dyes and UV-blocking agents that may be present in the polarizer film or adhesive layers.
Those prior-art polarized sunglass lenses which relied upon UV-absorbing dyes added to the polarizer film and/or adhesive layers are subject to a loss of UV protection if these dyes degrade when subjected to frequent and prolonged exposure to high-intensity direct sunlight, as sunlight contains a substantial amount of harmful UV light. UV-induced damage to polarizer dyes can also cause some prior-art polarized lenses to exhibit visible tint discoloration or fading under similar conditions. This is certainly not a desirable trait in sunglass lenses.
U.S. Pat. No. 6,773,816 by Tsutsumi is also of some relevance. Some embodiments of the Tsutsumi didymium glass filter as disclosed are able to block UV light and near-UV light in the range of 380 nm to 400 nm. However, the disclosed examples exhibit such low transmittance of certain blue, green, and/or red wavelengths as to interfere with accurate color perception.
It would be very beneficial for a polarized sunglass lens to provide enhanced perception of all visible colors while blocking dangerous UV and near-UV light and providing substantial, permanent, non-fading absorption of destructive UV light in the front lens element to protect the polarizer film and adhesive layers from UV-induced discoloration, fading, or other degradation.